Summary
Although many oil reservoirs are producing crude oils of different sulfur
and asphaltene contents, deposition problems of sulfur and asphaltene
components in porous media are investigated separately. The major objectives of
this laboratory study are to investigate the simultaneous deposition of sulfur
and asphaltene in porous media. To achieve these objectives, the influences of
the following on the permeability damage of the reservoir rock were
experimentally investigated: (1) crude-oil flow rate, (2) permeability of
reservoir rock through which crude oil flows, and (3) concentrations of sulfur
and asphaltene in the crude oil.
A base run was conducted using the crude oil after removing sulfur and
asphlatene. Ten dynamic flow experiments were carried out using different crude
oils of different sulfur and asphaltene concentrations and under different flow
rates. The crude oil was flooded through different rock permeabilities of 2.34,
6.23, 16.58, and 21.48 md and under different flow rates of 0.5, 1.0, 2.0, and
3.0 cc/min, respectively. No permeability reduction or pore plugging was
measured for the base experiment. The results indicated that the increase of
flow rate increases the formation damage because of simultaneous deposition of
sulfur and asphaltene in the reservoir rock. Core samples of lower permeability
showed more severe permeability damage than those of higher permeability for
the same applied flow rate and the same sulfur and asphaltene content of the
crude oil. Furthermore, the increase of asphaltene and/or sulfur content of the
crude oil increases the rock damage.
The attained results of this study highlighted the important role of
formation damage of carbonate oil reservoirs containing oils with a
considerable amount of sulfur and asphaltene. In addition, the study provides
two empirical correlations capable of predicting the permeability damage rate
as a function of flow rate or initial rock permeability. These correlations
represent useful tools for semianalytical and simulation studies.
Introduction and Review
Almost all deep sour-gas reservoirs contain elemental sulfur as a dissolved
species. Reduction in pressure and temperature induced sulfur precipitation by
a reduction in the solubility of the sulfur in the gas and/or oil phase beyond
its thermodynamic saturation point. These changes occur during production
operations and can result in sulfur deposition in the reservoir, wellbore, and
surface facilities. Deposition of elemental sulfur in the near-wellbore area
may significantly reduce the inflow performance of sour-gas wells. In addition,
oil reservoirs all over the world suffer from simultaneous sulfur and
asphaltene deposition problems in porous media, which cause problems in
production facilities. Investigation of sulfur deposition in porous media
receives little attention, while asphaltene nature and deposition in porous
media have been covered extensively. Furthermore, the investigation of
simultaneous sulfur and asphaltene deposition has not been studied in spite of
the expected problems of formation damage and facility corrosion.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
27 October 2004
- Revised manuscript received:
7 April 2005
- Manuscript approved:
15 April 2005
- Version of record:
20 February 2006
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